Control circuit for signal recording and reproducing systems



April 13, 1948. 5. J. BEGUN 2,439,446

CONTROL CIRCUIT FOR SIGNAL RECORDING AND REPRODUCiNG SYSTEMS Filed Nov.29, 1944' s Sheets-Sheet 1 DIFFERENT/MI tlcflf/e fiHPL/FIER mrzsmmOSCILLATOR AMPLIFIER Ann/HER Couu'rn 4 /-I8 I z AMPLIFIER I I l7 9SIGNAL (insure: RECTlF/ffi SEMI JOSEPH Bseuu Arro April 8- s..;. BEGUM 72,439,446

CONTROL CIRCUIT FOR SIGNAL RECORDINQ AND REPRODUCING SYSTEMS Filed Nov.29, 1944 s Shee t s-Sheet z ELECTRON/k RELAY dill- 1 Drnanuurox Tm:DELAY Nsr Won:

INVENTOR. 55m Joszrn Bzeuu ATT RNEY April 13, 1948.

CONTROL CIRCUIT FOR SIGNAL RECORDING AND REPRODUGING SYSTEMS Filed Nov.29, 1944 S. J. BEGUN 3 Sheets-Sheet 3 OscILI. 1mm 1 OscILLIInR ZAMPLIFIER FILTER RECTIFIER 5mm. 50mm:

"FIG 5 55m JosEPII Bzeuu Hrromusy Patented Apr. 13, 1948 CONTROL CIRCUITFOR SIGNAL RECORD- ING AND REPRODUCING SYSTEMS Semi Joseph Begun,Cleveland Heights, Ohio, as-

signor to The Brush Development Company, Cleveland, Ohio, a corporationof Ohio Application November 29, 1944, Serial No. 585,736

2 Claims. (Cl. 234-) My invention pertains to control circuits for usein signal recording and reproducing systems such, for example, as themagnetic, optic or mechanical systems.

This application is a continuation-in-part of my application Serial No.455,646, which has issued as Patent Number 2,370,134.

An object of my invention is to provide a control circuit for a signalrecording and reproducing system wherein the reproducing circuitexercises a function on the recording circuit.

Another object of my invention is to provide a control circuit forsignal recording and reproducing systems wherein the reproducing'circuitexercises a function on the recording circuit after an adjustable timedelay.

A further object of my invention is to provide a control circuit as setforth in the next above object wherein the amount of delay may beadjusted by a number of diiierent means.

Still another object of my invention is to pro-- vide a method ormeasuring distance or time by a signal recording and reproducing system.

It is also an object of my invention to provide a control circuit for asignal recording and reproducing system wherein the reproducing circuitis energized only while reproducing a. recorded signal to cause therecording circuit to become inoperative.

Other objects and a fuller understanding of my invention may be had byreferring to the following description, claims and drawings, whereinFigure 1 illustrates a time interval measuring system utilizing myinvention.

Figure 2 is a simplified schematic diagram of my invention.

Figure 3 is a block diagram of a device utilizing my invention.

Figure 4 is a schematic block diagram of another form of my invention,and 1 Figure 5 is a block diagram illustrating still another form of theinvention.

In Figure 1 there is shown a disk I of magnetizable material which isrotated at a known and constant rate of speed by a motor 46. Associatedwith the disk I!) are two magnetic recording heads 41, 48, and tworeproducing heads 49, 50. The recording head 41 and the reproducing head49 are located on track A on the disk l9, and the reproducing head 49 isadapted to "pick-up the signal which the recording head 41 impresses onthe disk, and the recording head 48 and reproducing head 50 are on trackB and are adapted to cooperate in the same manner as heads 41, 49. Anobliterating head 5| is positioned between the reproducing head 50 andthe recording head 49,

and extends only across track B, thus preparing the track for a newrecord. The reproducing head 48 also serves part time as an obliteratinghead.

When a time interval is to be measured the motor 48 is started and thedisk I0 is driven at a known and constant rate of speed. Switches 52, 53and 59, are normally in the positions shown by dotted lines, switches 52and 59 being open. At the start of the interval to be measured theswitch it is thrown by external means to the left thereby closing allthree switches 52, 53 and 59. Closing switch 52 connects the outputsignal from the oscillator 54 through the amplifier 55 to both recordingheads 47, 48. Closing switch 53 connects the battery 56 to the head 49thereby making head 49 an obliterating head. Closing switch 59 conmeetsthe output irom a differentiating circuit ii to a counter device 51.Trigger circuits of the general type which would be operable to actuateswitch 96 are shown schematically in United States Patent Number2,378,389, issued to S. J. Begun on June 19, 1945, forRecording-reproducing device, and in detail in United States PatentNumber 2,378,388, issued to S. J. Begun on the same date, {or Recordingand reproducing device. A trigger circuit having input connections forfive difierent types of input signals is shown in detail in UnitedStates Patent Number 2,395,127, issued to Otto Kornei on February 19,1946, and assigned to the same assignee as the present inven tion.During the time that it takes the disk in to rotate through the angle a:both of the recording heads 41, 48 are recording the signal from theoscillator 54. When the magnetic pattern of the signal recorded by head48 on track 13 reaches the reproducing head 59, an electromotive forceis generated which is amplified by the amplifier 58, and the outputthrough the rectifier-integrator Hi, the diflerentiating circuit H andthe switch 59 is used to actuate the counter 51 and the output from therectifier-integrator I0 is also used to reduce the gain in the amplifier55 to prevent the heads 41, 48 from further recording for an interval oftime t equal to the length of time it takes the disk to rotate throughthe angle a. Patent Number 2,378,388 described in detail how the gain ofan amplifier connected to a magnetic transducer-head may be reduced toprevent the recording head from recording on a moving magnetic member.When the magnetic pattern which was recorded on track A reaches the head49 it is obliterated by magnetic flux set up by current from the battery55.

Accordingly, reproducing head 50, after the start of an interval to bemeasured, does not pick up any signal for the time t, which is the timenecessary for the disk ID to rotate through the angle 02. Then for aperiod of time t it picks up a signal. For the next period t no signalis picked up etc. It will be seen, therefore, that the head 5|] picks upa signal in the time intervals t to 2t, St to 4t, St to (it, etc., butdoes not pick up a signal in the time intervals to t, 21. to 3t, 4t toSt,

etc.

From the amplifier 58 the signal passes to a rectifying and integratingdevice ID to establish substantially a D. C. pulse having a durationcorresponding to the duration of the alternating signal. This D. C.pulse blocks amplifier 55 and is also fed to a difierentiating device H.The outut signal from the differentiating device consists of a series ofpulses occurring at time intervals t, 2t, 3t, 4t, 5t, etc., and eachpulse causes, by means of an electromagnet or the like, the counter 51to move one step for eachperiod of time during which the disk rotatesthrough the angle a. The counter which is a special Veeder-Rootstep-by-step type of counter wherein the usual numbers 1, 2, 3, 4, etc.,are replaced by the indications 0+, 2-, 2+, 4- etc., starts with areading of 0 and the first pulse causes the counter to indicate 2(), thesecond pulse actuates the counter to cause it to indicate 2(+), and thethird pulse causes the counter to indicate 4(-) etc. Unless the intervalto be measured is exactly as longas the length of time for a whole evennumber of revolutions of the disk l0 through the angle a there will be asignal recorded on track A which has not been obliterated by the head49. The duration of this signal must be added to or subtracted from theinterval indicated on the counter 51. The duration of this signal willbe indicated on the scale of the indicating device 24, and will besubtracted from the counter indication if the counter says and added tothe counter indication if the counter says The reason for the counternotation O(+), 2(-)-, 2(+), etc., is as follows: The time interval fromzero microseconds to something just less than t microseconds (t=time fordisk to rotate through angle a) is measured by determining through whatangle on the disk ID a signal has been recorded. As there has been nowhole time interval t the counter reads 0 and the interval must be addedto 0 to get an accurate reading; hence the counter notation 0(+). For atime interval longer than it but less than 2t the duration isdeterminedby reading the counter 51 which has been actuated once and byreading the meter 24 which indicates the angular amount of signal whichhad been applied to the disk throughout the first time interval t andwhich had not been erased by obliterating head 49 during the second timeinterval it. Remember that the device operates to record a signal duringthe first, third, fifth, etc., intervals t and to erase the recordedsignals during the second. fourth, sixth, etc., time intervals t, andthat while it is recording it is not erasing and while it is erasing itis not recording. It will be appreciated, therefore, that during thesecond interval t the time interval (less than t) which remainsunobliterated on the disk 10 must be subtracted from the counterindication, and if the counter indicated 1 the reading would be inerror. Hence the counter is made to indicate 2() to show that the meterreading must be subtracted from the counter indication.

The head 49 serves as an obliterating head only during the interval tobe measured. During the first time interval tthe obliterating head 4 49will be energized by the battery 56 but will not obliterate a signalfrom track A as there is no: signal recorded on that portion of track Awhich is passing head 49. During the second time interval t the head 49will obliterate the signal from track A. During the third time intervalt there will be no signal obliterated. etc.

At the end of the time interval to be measured the switches 52, 53, and59 are simultaneously thrown by the trigger circuit, switches 52 and 59returning to their open position and switch 53 connecting the head 49 toa meter 24. The head 49 thereafter functions as a reproducing headinstead of an obliterating head. Opening switch 52 breaks the connectionbetween the oscillator 54 and the recording heads 41, 48 therebyterminating all recording. Opening switch 53 breaks the connectionbetween the battery 56 and the obliterating head 49. Switch 59 breaksthe circuit from reproducing head 50 to the counter 51 in order thatthere will be no further actuation of the counter which could arise fromthe end of the signal recorded on track B passing through the head 50.Without switch 59 the signal, if it occurred sometime during 2, 4, 6, or8t, would establish a pulse which would actuate the counter 51. therebyintroducing an error. It is the function of the trigger circuit switchIE to make certain aforedescribed circuit connections at the start ofthe time interval to be measured, and to break those circuit connectionsand make other aforedescribed circuit connections at the end of the timeinterval to be measured. During the time interval certain recording andobliterating functions take place from which it is possible toaccurately measure the duration of the time interval, whether it be onlya few microseconds or much longer in extent.

For reasons of simplicity I have shown switches 52, 53, and 59 asmechanical and actuated by the trigger circuit switch I6, but it is tobe understood that electronic switches may be used, as a more rapidaction could be obtained thereby reducing the amount of error due totime lag in switching. The details of the actual mechanism utilized tothrow the switch iii are not shown as they form no part of thisinvention and any one of a large number of mechanisms well known to theart may be utilized. For example, if the extreme accuracy of mymechanism is not required, the switch l6 could be thrown by hand, muchin the same manner as a stop watch is utilized. However, if the inherentaccuracy of my device is to be utilized more fully a much more accuratemeans and method should be used, and such a means and method is shown inFigure 2 where a mechanical switch [4 is electrically thrown by asolenoid I9, 20. A still further improvement is schematicallyillustrated in Figure 3 wherein electronic switches or relays areutilized.

The signal which was recorded on track A and was not obliterated by head49 before switch 53 was opened will, upon repeated rotation of the diskpast the pickup head 49, establish an electromotive force. Theelectromotive force is ampli'fied by the amplifier 2|, and passesthrough the limiter 22 and the detector 23, and is applied to thecalibrated current averaging device 24.

The time interval is measured by the operator algebraically combiningthe readings on the counter 51 and meter 24. The counter indicates wholetime intervals t, and the meter 24 indicates a portion of a timeinterval t. The meter indication is to be added to the counterindication if the counter says and is to be subtracted from the counterindication if the counter says In order that my device may be clearlyunderstood the successive operations will be described in connectionwith measuring a given interval. For example: Suppose it is desired tomeasure an interval of 275 microseconds, and the time of one revolutionof the disk II is 100 microseconds. It is apparent that the time for thedisk to rotate through the angle a, it a equals 270 degrees, is '75microseconds. Before the start of the interval to be timed switches 52,-II, and 59 are open, the disk In is rotating, tracks A and B are erased,and the oscillator 54 is operating.

At the start of the interval to be measured switches 52, 53, and 59 aresimultaneously closed thereby connecting the counter 51 (which registersto the reproducing head 50 and connecting the battery 58 to the head 49to establish it as an obliterating head, and connecting the oscillator54 to the recording heads 41, 48 to simultaneously initiate recording onboth tracks A and B. After 75 microseconds the front of the record ontrack B starts to pass reproducing head 50 thereby simultaneouslyinitiating two actions. One action causes the counter 51 to change itsreading from 0+ to 2-, and the other action causes the amplifier 55 tobe blocked to stop the recording on tracks A and B. As long as arecorded signal passes head 50 there will be no recording by heads 41,48 as the blocking of amplifier 55 continues. At the same instant thatthe start of the signal on track B reaches reproducing head 50 the startof the signal on track A reaches the obliterating head 49. The record ontrack A will be obliterated by head 49 for 75 microseconds until the endof the signal on track B passes head 50, at which time amplifier 55 isunblocked and recording is again started at heads 41, 48, and thecounter 81 is actuated to read 2+. By this time 150 microseconds haveelapsed. The obliterating head II erases all records which pass underit. For the next '75 microseconds heads 41, 48 record on tracks A and Band when the front ends of the records reach heads 50 and 49 the counteris moved to 4- and the recording by heads 41, 48 is again blocked. 225microseconds have now elapsed. For the next 50 microseconds until theswitch 53 is opened by trigger circuit I. at the end of the interval tobe measured the obliterating head 49 obliterates the record on track A,thereby leaving a record only 25 microseconds long on track A. The endof the interval to b measured also opens switches 59 and 52. Switch 53,upon being thrown by trigger circuit It, connects the head 49 to themeter 24 and it now functions as a reproducing head. Upon repeatedlyreproducing the record remaining on track A the meter 24 will indicate25 microseconds, and because the counter read 4- the 25 microsecondswill be subtracted from 300 microseconds (4X75=300) to give an intervaltime of 275 microseconds.

A condenser discharge type of obliterating device may be provided forrendering the magnetic condition of track A uniform before a newinterval is measured. Normally the switch is open. After an interval hasbeen measured and the operator desires to clear track A, he presses pushbutton I6 thereby closing switch I! and connecting the battery I8 to thecoil of the obliterating head I9. The current from the battery I8 issuiilcient to saturate the portion oi the disk I0 which is under theobliterating head 19 and is applied for at least one revolution, andwhen the push button is released the condenser TI, which has beencharged by battery 18, discharges through th coil of the obliteratinghead thereby gradually r lucing the flux which is applied to themagnetizable disk III. This type of obliteration due to the condenserdischarge does not leave a sharp change in the amount of magnetizationin the portion of the disk which was under the head I9 when the switchwas opened, thereby preventing the actuation of the counter 51 by thesharp change in magnetization.

In Figure 2 there is shown a length of magnetic wire or tape III whichis driven in the direction 01' the arrow II by any suitable drivingmeans such as the variablespee'd motor M. The length of magnetizablematerial I0 may be endless as shown or it may be in the form of a lengthof round or flattened wire wound on one or more reels. A magneticrecording head I2 is positioned in magnetic flux linkage relationshipwith the magnetizable member III and is electrically connected to asignal generator I3 which is preferably an alternating signal generator,but may be a direct current generator. A switch I4 is in the circuitfrom the signal generator I3 to the recording head I2.

A magnetic reproducing head I 5 is positioned in magnetic flux linkagerelationship with the magnetizable record member I0 and is positioned adistance away from the recording head I2 in the direction of the motionof the record member. This distance between the heads is adjustable overa wide range. The reproducing head I5 is electrically connected to anamplifier I8 the output of which passes through a rectifier and isconnected to a solenoid IS.

The plunger 20 of the solenoid is biased to normally keep the switch I4closed so that the recording circuit through the recording head I2 isclosed. Upon the start of the signal which has been recorded on themagnetizable member I0 by the recording head I2 passing the reproducinghead I5 the solenoid winding I9 is energized by current derived fromamplifier I8 and the rectifier. The solenoid plunger 20 is therebyactuated causing switch I4 to open and break the circuit to therecording head I2 with consequent termination of the recording. Upon theend of the signal which has been recorded on the magnetizable member IDpassing the reproducing head I5 the solenoid force is removed and thenatural bias on the 'plunger 20 of the solenoid causes the switch I4 toclose thereby remaking the recording circuit so that a further recordingon the magnetizable member I0 is made possible. The plunger of thesolenoid I9 is also connected to a counter mechanism I! for actuatingthe counter each time it opens the switch I4.

By utilizing this system a signal will be recorded on the first length Dof the magnetizable member and the next portion of the magnetizablemember of length D will have no signal recorded on it. The third portionof length D will have a signal recorded on it and the fourth portion oflength D will again have no signal recorded on it. The length of time Tnecessary for an incremental portion of the magnetizable member I0 totraverse the distance D depends upon two factors. The first is thedistance D between the recording head I2 and the reproducing head I5 andthe second is the rate of motion of the magnetizable member ID. Changingeither one of these factors will change the time interval T.

Accordingly, altering the speed at which the magnetizable member ID isdriven, or changing the spacing D of the heads I! and I, or bothtogether will alter the time delay T. As has previously been stated, thecounter mechanism I] will be actuated each time an incremental portionof the magnetizable member which has the beginning of a recorded signalpasses the reproducing head l5.

This device could be used to measure time intervals by energizing thegenerator l3 during the interval to be measured. Under these conditionsthe speed of the magnetizable member Ill must be known and must beconstant and the distance D must be known. From the counter indicationthe time interval can be determined with any desired accuracy, the errorbeing always less than the time interval 2t. The same device can also beused to measure the length of the record medium. This measurement isindependent of the speed of the member i0, the error will not exceed 2D.Thus, if the system is to be utilized as a distance measuring device,the indication on the counter mechanism multiplied by the distance 2Dwill indicate the total amount of the magnetizable member which haspassed the reproducing head i5.

A measuring system of this kind is valuable where it is desirable towind onto a reel 9. definite amount of magnetizable member. For example,it may be desired to wind 5,000 feet of wire onto a spool or reel. Thedistance between therecording head I2 and reproducing head l5 may be setat 5 feet. When the counter mechanism ll indicates 500 then 5,000 feetof wire has been wound onto the spool or reel.

Automatic control circuit means 9 are provided for stopping the motorwhich is driving the wire at the end of any adjustably set amount onthecounter I1, and suitable obliterating means may be associated with themagnetizable member i0. It is also within the scope of my invention thatelectronic means may be used to make and break the connection betweenthe generator l3 and the recording head l2.

Figure 3 is a block diagram illustrating the use of my invention inconnection with a transient recorder somewhat similar to the type shownand described in my copending application Serial No. 425,304, fliedJanuary 1, 1942, which has issued as Patent 2,378,388.

The pole pieces of the recording and reproducing head (referencecharacters l2, ii) are shown offset for use of the longitudinal methodof recording, but it is to be understood that the perpendicular andtransverse methods which are well known alternatives may also be used.The recording head I2 is supplied with carrier current from anoscillator tuned to 5,000 cycles.

The oscillator 25 is arranged to be frequency modulated by thetransient, but before occurrence of the transient unmodulated carrier isrecorded on the tape or wire I0.

The tape 10 passes almost directly from the recording head l2 to anobliterating head 28. Within the obliterating head the newly recorded5,000 cycle unmodulated carrier is removed by the action of a strongalternating field supplied by current from a kc. oscillator 21. Most ofthe tape, including that part passing through the reproducing head i5,therefore, is kept in a demagnetized state and as a consequence, thereis no carrier output from the reproducing head.

The transient input terminals 28, 29 are connected to the modulatorinput and to an elec-' 8 tronic relay 30. When atransient signal occursin the test circuit connected to the input 28, 29, it frequencymodulates the 5,000 cycle recording carrier. The start of the transientsignal also actuates the electronic relay 30 which immediately shuts offthe obliterating circuit to the obliterating head 26 so that the newlyrecorded frequency modulated carrier, plus the bit of unmoduiatedcarrier that existed between the recording and the obliterating heads i2and 26 at the moment the transient started, are not obliterated.

Now that the obliterating process has stopped, one element of the tapeapproaching the reproducing head i5 has on it the beginning of therecordedcarrier (corresponding to the point at which obliterationstopped) and when this element reaches the reproducing head, the varyingmagnetic pattern on the tape induces in the head a corresponding carriervoltage; As soon as this carrier voltage appears, a second electronicrelay 3| is energized. The relay 3| applies a predetermined D. C.potential to a time delay network 32. As the tape element bearing thebeginning of the carrier progresses from the reproducing head i5 back tothe recording head i2, the voltage across the output of the time delaynetwork 32 builds up and just as the tape element bearing the firstrecorded cycle of the carrier arrives at the recording head, the timedelay network develops suflicient voltage to actuate a third electronicrelay 33 which shuts off the recording circuit. Thus recording of thecarrier is automatically shut off just as the tape length is fullyrecorded.

The pulleys on which the tape or wire i0 is mounted are arranged so thatvarious lengths may be accommodated. The distance from the reproducinghead i5 back to the recording head I2 may be fixed. Thus a single timedelay adjustment suffices for all tape lengths. The distance between theheads may be variable but then the amount of time delay of the timedelay net-'- work 32 must also be correspondingly variable. Various tapelengths may be accommodated by shifting the pulley 34 at the other endof the loop.

During reproduction the tape loop is repeatedly driven past thereproducing head 15 so that the output of the head consists of a carrierfrequency modulated in accordance with the original transient, whichcomposite signal is repeated once for every revolution of the tape. Thecarrier output of the head is demodulated by the demodulator 9 so thatfacsimiles of the original transient are repeatedly reproduced at theoutput terminals 8. This signal may be observed on a. cathode rayoscillograph having a sweep circuit synchronized with the rotation ofthe tape as is shown by United States Patents 2,378,388 and 2,378,389.Thus the transient recorder converts a transient which cannot readily beobserved on a cathode ray oscillograph into a continuous sequence ofsignals each of which is a facsimile of the transient. This continuoussequence of signals is readily observed on an oscillograph in'conventional manner or applied to analyzing apparatus; and the controlcircuit, which operates through a time delay circuit in addition toutilizing the inherent time delay necessary for an incremental portionof the tape to move from the recording head l2 to the reproducing headl5, functions to assure that substantially the entire length of tape isavailable for retaining a useful record.

In the three previous exemplifications of my invention I show that asignal picked up by the reproducing head controls the on and offrecording operation of the recording head with a time delaycorresponding to the distance between the recording and reproducing headand to the speed of the recording medium. It should be understood thatthe scope of my invention is not limited to stopping and starting therecording process, as it is applicable to any system in which the pickuphead controls in any way the recording characteristics of the recordinghead.

For example in the system shown in Figure 4, instead of using onegenerator, two oscillators 35, 36 generating different frequencies maybe provided, either of which supplies current to the recording head 37in accordance with a time sequence. The amplifier 39, cooperating withthe pickup head 38, may be so arranged by suitable filter networks 40 asto pass one frequency but to reject the other frequency. The signal ofthe one frequency which passes through the filter 40 will afterrectification by the rectifier 4i control a'relay 42. The relay 42actuates switch 42' and when it is in its normal position it connectsthe first oscillator 35 to the recording head 37 and when in itsotherjposition it connects the second oscillator 36 to the recordinghead 37. Since this second frequency is not passed by the filter 40 therelay 42 will return the switch 42 to its normal position connectin thefirst oscillator 35 to the recording head 31. The relay therefore willact in the same manner as it would have acted had there not been anysignal recorded on the medium by the second oscillator.

In another form of my invention, shown in Fig. 5, the recording head 43may be supplied from one source 44 with signals of different intensitylevels. As long as a relay45 holds switch 45 in its normal or closedposition the source 44 supplies the full recording level, However, whenthe relay 45 is energized to cause the relay 45 to open the switch 45'the recording level is reduced by a predetermined 'amount as it passesthrough the attenuator 60 to the recording head 43. The signal recordedwith the reduced level,

when picked up by the reproducing head 46, is

not sufiicient to supply the necessary operating current to cause therelay 45 to operate switch 45'. In such a system as just described thesignal may consist of one frequency or may contain different frequencycomponents.

The system which has just been described may be used for monitoringpurposes, particularly if the signal source supplying the recordingsignal changes its level substantially so that it exceeds the volumerange of the recording medium. An arrangement is provided in which byautomatic means the recording level is reduced to the point where nooverloading takes place. In this system shown in Figure 5, theattenuator 60 is connected into the recording circuit to reduce therecorded level to the desired amount and a gain control is provided inthe reproducing amplifier 62 to compensate for the reduction in therecording level. When the signal source 44 generates a signal at a highlevel and this high level signal is recorded unattenuated through switch45' the high level signal which is picked up by the reproducing head 46is supplied to the control relay 45 which opens switch 45' therebycausing all of the recording signal to go through the attenuator 60.Actuation of the relay 45 also increases the gain of the reproducingamplifier 62 through gain control 8|. When the level of the signalsource,

after attenuation, drops to such an extent that the signal impressedupon the signal carrier l0 reduces the signal-to-noise ratio in anundesirable manner, the relay 45 causes the attenuator E0 to beshort-circuited and the full energy of the signal source is supplied tothe recording head 43. This is automatically done in this system sincethe low voltage generated by the low level signal in the reproducinghead is not sufficient to generate the current for energizing the relayand the relay returns to its normal position. The relay, therefore,releases its contact switches causing switch 45' to short-circuit theattenuator 50 in the recording channel and causing switch 6 l to changethe gain in the reproducing amplifier to compensate for the increasedrecording level. The switch 6! may be utilized to connect to ground aresistor between two stages in the amplifier 62, thereby altering thegain of the amplifier.

While I have shown and described my invention with a certain degree ofparticularity, it is to be understood that numerous changes in thevarious component parts and their arrangement may be made withoutdepartin from the spirit and scope of my invention as hereinafterclaimed.

I claim as my invention:

1. A control system comprising, a, record member, means for moving saidrecord member, normally closed signal recording circuit means includingrecording head means, signal reproducing circuit means includingreproducing head means spaced apart from said recording head means alongthe path of motion of said record member, circuit opening means in saidnormally closed signal recording circuit means, electrical circuit meansinterconnecting said signal reproducing circuit means with said circuitopening means for opening said circuit only while said signalreproducing means reproduces a signal recorded on said record member,and means for moving at least one of said head means with respect to theother head means for altering the time delay between the recording andthe reproducing of a given signal on said record member.

2. A control system comprisingya record member, means for moving saidrecord member, normally closed signal recording circuit means includingrecording head means. signal reproducing circuit means includingreproducing head means spaced apart from said recording head means alongthe path of motion of said record member, circuit opening means in saidnormally closed signal recording means, electrical circuit meansinterconnecting said signal reproducing circuit means with said circuitopening'means for opening said circuit only while said signalreproducing means reproduces a signal recorded on said record member,and means for changing the rate of motion of said record member foraltering the time delay between the recording and the reproducing of agiven signal on said record member.

SEMI JOSEPH BEGUN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

